The present invention relates to encapsulated digital electric position measuring apparatus and, more particularly, to a position measuring apparatus having a scanning component screened by a flexible covering band.
Digital electric position measuring devices are well-known in incremental and absolute length and angle measurement systems. Such measurement systems include at least one measuring scale having periodic grid divisions which are detectable by a scanning component. The scanning component may use photoelectric, inductive, magnetic, capacitive, or other types of sensors to detect the grid divisions. To avoid interference, especially by fouling of the grid divisions and/or the scanning component, such measurement systems have in the past been tightly encapsulated against dust and spray.
In incremental measurement systems using incident light or transillumination, a known practice to avoid fouling is to provide the grid divisions and portions of the scanning component within an elongated housing which is covered by a flexible steel band to exclude dust and spray. In one zone, the steel band slides over a curved surface of the scanning component projecting from the housing; outside this zone, the steel band is secured to the housing with sealing effect by means of magnetic strips arranged laterally on the housing. (West German DE-PS No. 2 207 374 and West German DE-OS No. 2 642 443.)
In U.S. Pat. No. 3,742,609 and in West German DE-EM 79 22 890, a slide gauge is provided with a flexible covering band which slides over the scanning component. The covering band is held against the portion of the carrier of the measuring scale to be shielded by tension on the covering band and by guides on a movable slide block.
A further known practice in encapsulated incremental position measurement systems is to house the grid divisions and portions of the scanning component within an elongated housing which is covered by a circulating flexible steel band guided in a groove. In such systems, the ends of the circulating steel band are fastened to the scanning component. Upon moving the scanning component along the carrier body, the steel band is circulated over rollers that are provided at the ends of the housing. (Teledyne Gurley Company publication "Pathfinder", No. 8780-75-879.)
Circulating, endless band-type coverings of steel or plastic have already become known in slide gauges for the purpose of protecting portions of the measuring scale. (West German DE-OS No. 1 806 935.)
Known encapsulated position measurement systems are expensive, especially due to the construction required to position the grid divisions, scanning component, and covering band in proper relationship. Also, measurement systems encapsulated in such a manner are often difficult to accomodate in applications having tight space limitations. It is, therefore, a general object of the present invention to provide an encapsulated digital electric position measuring apparatus having a simple and economical construction and wide versatility.